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I am aware that DSLRs are able to correct colour temperature either automatically or by presets. But as I move closer to taking the plunge into either a D2x or an EOS1DS MkII I am intrigued by some aspects of colour correction that I have read about.

Let me, for a moment, har back to my practice with film: I use a Colour Temperature meter at all times and use CC or LB filters. A spot of empirical knowledge creeps in and I do not necessarily always apply as much correction as indicated. The results are fabulous.

Now, as I understand it, in an extreme case- especially where Tungsten light calls for the addition of a great amount of BLUE that the extra levels of blue can lead to extra noise in the blue channel. It would not phase me at all to continue to use filters and my meter - I know of many other high-end commercial shooters who do. (In fact, a couple of mates who had bought MF digital backs and placed their Colour Temperature meters on consignment sale went and got them back once they became aware of the issues.)

So what is the concensus of opinion amongst the high-end users here? Adding an 81C amount of red and yellow I don't see as a problem but adding a conversion level of blue could be.

I might add that aesthetically there is also reason to make readings with the CT Meter. A colour shift may not always need to be GLOBAL and a correction for just a specific area of the image may be needed. I know from years of doing so that it is a technique that works incredibly well on film - I'm just hoping for some clues about how it might be with digital capture.

Thanks,

A friend of mine who would be a high end shooter needed an area in his studio to shoot "daylight" shots. I installed several (3) double bank 40watt Hitachi 40 FL40S-N-EDL-NU tubes. I have no idea of the technicals but this system was as close to natural daylight as is available using artificial means. The tubes are used in high attention to detail printing facilities where colour accuracy in imperative. These tubes are not generally available to the consumer. A supplier will get them in if bulk numbers are ordered. Here in Adelaide we had to arrange a group purchase through an arts school. the tubes were about $20Australian each.
Hope this helps
I'm a "lo-end newbie"

Sheetshooter - there are a few factors that must be taken into account when changing from film to digital.

In digital always shoot RAW - this gives you a negative that can be manipulated far more than film could ever be, and it’s in real time. Couple this to an AdobeRGB LCD monitor that is calibrated every month - by this I mean a true RGB monitor and these are not cheap ($5k plus) or, conversely, a very good CRT. Add to this a knowledge of using the PP program beyond darkroom skills. With the monitor we are dealing with transmitted light whereas a polaroid shows reflected light.

For pack shots I use Bowens Trilites that are calibrated for daylight but I have also enabled a WB within the camera for these shots in the cocoon.

With due respect to old time film users (me included) the transition to digital is not a given thing - it is a total new world of computers, monitors and a different mind set - luckily I started on this course in the middle 80’s and I still learn something new every day. . .

In dealing with CRW/NEF raw capture, the process as Chris outlined of WB/colour correcting in PP is in fact subject to the limitations Sheetshooter brought up - it is attenuating the blue and red channels with the green to match what the eye perceives. Thus, if there is objectively significantly less amounts of say blue (due to lighting), the sensor's captured levels of blue would suffer and as mentioned it will be more noisey in the blue channel.

The corrective procedure above really amounts to effectively turning up the gain in one or more colour channels, much like shooting at high ISO equivalent setting would do (to all channels)... thus any noise characteristics inherent within the sensor will be exposed.

I believe the use of optical filters is the way to go. What's more, the individual colour histograms of Nikon and the Xerox competitor's flagship models will be a godsend in this case, aiding in optimising signal to noise ratios. BTW, how much are colour temperature meters? Do they work under artificial illuminations such as sodium vapour lamps?

Here you go Onyx -

http://www.bogenimaging.us/

Gossen and Minolta are, as far as I know, the only manufacturers of temp meters

So much to learn.....
I hope I don't come across as a thread hijacker or anything but this question seems appropriate here...

How much noise on the blue channel are we talking of here?

I have a little project I've been putting off but must get back to. I have quite a number of oil paintings I wish to photograph so I can catalogue them and make a web site (eventually) advertising them.

I have tried setting up my flash units in various ways including umbrellas and really acute angles, but I seem to always end up with hot spots reflecting from certain points on the shiny oil paint.

I figured the best way around my problem was to indeed use real daylight (not direct sunlight), which brings in a bit of a logistical challenge for me, not least of which is the weather here in Tassie.

If I can use normal room lights and adjust the camera settings to compensate, then I will have a far easier solution, but with these concerns of interference or distortion to the blue channel, perhaps that's not the best solution. If the blue distortion / noise is minor to the point it won't make a noticeable difference, that could be a solution.

My options -
Shoot in real daylight
Shoot with normal room lights and adjust white balance to incandescent
Shoot with normal room lights and buy a filter (which one?)
Persist with the flash units
Something I haven't thought of

Any ideas / suggestions?
Adam. PS my 100th post WOOHOOOO!!

Adam,

How big are the paintings? Have you considered a light tent?

About 300 paintings all 900 x 600 mm
About 100 paintings all 500 x 400 mm

One of the smaller ones here

I need to search and find what a light tent is. I've heard of it but probably have an incorrect image in my mind of what it is. Is it suitable for paintings this big?

Ta.

Light tents come in a variety of sizes, but should be able to handle this task for you. They're not overly big, but large enough to warrant the use of a larger sized tent. The larger the tent, the greater the diffusion it will offer you. You may be able to even make one up for yourself, using some white translucent fabric over a suitable frame.

You can then illuminate the whole tent, with a painting located within the tent's confines.

Set up your camera to an appropriate copying location, noting that you may want to ensure that the film plane is parrallel to the subject and that an appropriate lens is in use.

You may wish to ensure that the fabric completely envelopes the painting, leaving just a small aperture for the lens to peek through. This should ensure minimisation of any possible hotspots.

Once you get your lighting right, this sort of job should be fairly mechanical and easy to complete - I would be presetting WB for the lighting and light tent, and likewise, playing with some test exposures till I was satisfied that everything was correct.

From that point on, your settings should be static from one image to the next, as the only thing that's changing is the subject matter, but everything else is constant.


As a side note, while light tents are available from some of the pro shops around Oz, their pricing is still in the "gee whiz, this is photographic gear so we need to charge an arm and a leg for it" range. While I was OS over Christmas, I purchased a medium sized one through Amazon for around US$60 and had it delivered to me in SoCal. It folds up into almost nothing and thus is very, very portable.

So it's worthwhile to investigate and look around.

One final question - that's a lot of paintings - is this a commercial job for you?

sirhc55 wrote:Here you go Onyx -

http://www.bogenimaging.us/

Gossen and Minolta are, as far as I know, the only manufacturers of temp meters

Gossen and Minolta are certainly the most highly visible makers of C.T. Meters at the general level - but there are others like Spectra in the motion picture industry and doubtless speciality industrial units that probably cost maga-bucks. I also had a Broncolor C.T. Meter for a time.

From the photographic viewpont there are essentially TWO types of meter in TWO styles.

TWO-Colour and THREE-Colour reading meters

Constant light only and Constant & Flash reading meters.

All the meters can give a reading of the Kelvinº but a TWO-Colour meters give a reading relative to correcting only red and blue while a THREE-Colour meter includes a display of Green and Magenta filtration for the correction of fluorescent tubes and discharge lamps.

Of course, any C.T. Meter is useless without a selection of the associated L.B. (light balancing) and C.C. (colour correction) filters.

Once I make my decision and purchase a camera of choice I shall be doing extensive testing to determine just how the digital system compares to using filters for precise correction. I shall post my findings, but it may be a month or so before I do that, so stay tuned if you are interested.

Cheers,

tasadam wrote:About 300 paintings all 900 x 600 mm
About 100 paintings all 500 x 400 mm

Ta.

Adam,

That is quite a daunting chore you have ahead of you.

In order to categorise the information I offer in a more useful way to others, I shall start a new thread on this subject for you.

Cheers,

gstark wrote:One final question - that's a lot of paintings - is this a commercial job for you?

No, my brother painted them and sent them all to me, he doesn't know how to market them and is sick of being ripped off, aslso he is short of storage space. I will get nothing for it, apart from the education of how to photo heaps of oil paintings...

Sheetshooter wrote:

tasadam wrote:About 300 paintings all 900 x 600 mm
About 100 paintings all 500 x 400 mm
Ta.

Adam,
That is quite a daunting chore you have ahead of you.

In order to categorise the information I offer in a more useful way to others, I shall start a new thread on this subject for you.
Cheers,

SheetShooter. I am sorry for getting your thread way off topic, I thought at the time and content of my original thread I was close to the mark with white balance etc. Now we're into tents, and probably going towards marketing. And like you say, for the benefit of all to learn from, it would be better suited to its own thread.

Gary and SheetShooter, lesson learned about keeping threads exactly to their intended subject. Where to from here? Do I start a new thread and paste threads from here or what?

Sorry, again
Adam.

By the way, Sheetshooter. When I saw your text under your applet, I thought it was a foreign address, not an equipment list... True, I did!
Now I have read posts in the other thread (poll) and understand when you say sheet (in Sheetshooter) you are referring to very large format film, and the list under the applet as gear that I won't ever dream of seeing, let alone using.

Ok Ok call me green...

Adam,

I started a thread for you this morning. it is in Tips and Tricks Forum with your name in the heading.

The information may be more complex than you need, but it is the good oil!

Cheers,

Back to the original thread. SheetShooter, Ive always wondered about this myself. The idea that filters arent needed due to availability of manipulation of WB in PP doesnt make sense to me in a lot of ways.

Surely, as with exposure etc, you want the best possible image sitting in your RAW image. As several have pointed out here, tuning the WB means altering the gain on the channels, which leads me to the question, what would the camera's 'ultimate' WB setting be? Where we are getting the best SNR out of each channel? We could then filter to that?? Sensible or not?? I guess the question is, are we going to lose more picture quality with the extra noise from the WB adjustment, or from filters?

Yes Robboh,

I think it is a really interesting point to follow up on. I shall ask my digital guru when next I see him. We were to have had a day of testing the Hasselblad and 22MP back today but a family emergency for him has interferred with that. I'll report back!